Justin Bieber has given an elderly fan a big boost in his battle against cancer after lending his support and urging him to "keep fighting".Peter Johngren was diagnosed with colon cancer in 2009 and it was during chemotherapy treatments that he stumbled across the Baby hitmaker's music online and discovered that the star's vocals helped to soothe his pain. Doctors have since found the 71 year old, a retired medic, is suffering from a separate case of advanced prostate cancer, but Johngren's daughter Emily Ward insists her father always lights up whenever he listens to or talks about Bieber. Johngren's sad story, which has featured in the local press in New York, has caught the attention of the teen pop idol himself, prompting the singer to reach out to his ailing fan. Bieber posted a link to a news report about Johngren on his Twitter.com page on Thursday (05Jul12) and wrote, "this guy is The Man!! Keep Fighting!! thanks!"